During year 9 of MH18343 research will continue to focus on the connectivity between various parts of the so&g bird brain involved in vocal control. We will also continue to explore the role of hormones in influencing the performance of vocal control pathways, and the relation between sex hormones and sexual dimorphism in the volume of vocal control stations of the telencephalon. We shall also start a study of computer aided description of Golgi stained neurons from the various vocal control stations, seeking microanatomical differences that might be correlated with the observed left hemispheric dominance and the learning of large song repertoires. These various approaches to the anatomy and physiology of brain pathways concerned with vocal learning are expected to yield basic insights into how the learning of new motor behaviors affects properties of the neurons involved.